South Korea and Japan reached a landmark agreement Monday on the thorny issue of wartime sex slaves that has long strained relations, Seoul's foreign minister said.

The deal would be "final and irreversible" if Japan fulfils its responsibilities, Foreign Minister Yun Byung-Se told reporters after talks with his Japanese counterpart Fumio Kishida.

Kishida said Japan agreed to offer one billion yen ($8.7 million) in state compensation for "comfort women" who were sexually enslaved by Japanese troops during World War II.

"The comfort women issue... occurred with the involvement of the Japanese military... and the Japanese government acutely feels its responsibility," he said.

Japanese Prime Minister Shinzo Abe expresses an "apology and repentance from the bottom of his heart" to the victims, Kishida said.

Seoul and Tokyo have been tussling over the wording of an agreement to settle the issue.

Up to 200,000 women, many of them Korean, are estimated to have been sexually enslaved by Japan during World War II. They were euphemistically known as "comfort women".

Protestors sit next to a statue of a South Korean teenage girl in traditional costume called the "peace monument" for former "comfort women" who served as sex slaves for Japanese soldiers during World War II, in Seoul on November 11, 2015